...also, so far I'm finding dungeons don't respawn. So find your own free home in the wastelands anywhere you want. Just clear out the baddies once and you're set. Perhaps I haven't played long enough, but so far I've noticed the containers that already have loot in them (in dungeons) don't respawn and the ones that were empty to start with (in dungeons) may spawn with loot at random once, but after that will remain the same?
Only one dungeon respawns on the interior (as well as exterior of course) but there is much speculation if it's a glitch or not, as the name of the location... ahem... stands out.
As for containers, for me on the 360:
All Nuka Cola machines, ammo boxes, first aid kits and player storage in the
game-designated housing will be safe all game, with the exception of the desk for me in the Megaton house. Some refrigerators in the wild are safe, but I test them with a single bullet and leaving the game cell for several days. All containers that had stuff in them originally, constantly respawn, but if I found something good the first time, it's always crap the subsequent times.